Reservoir simulation is an area of reservoir engineering which employs computer models to predict the flow of fluids, such as petroleum, water, and gas, within the reservoir. Reservoir simulators are used by petroleum producers in determining how best to develop new fields, as well as in generating production forecasts on which investment decisions are based in connection with developed fields.
Reservoir simulators numerically model the flow of hydrocarbons and brines in reservoirs and the flow rates of fluids through the pipes and devices that comprise the gathering and injection facilities for the reservoir. One of the primary factors affecting flow rates calculated by reservoir simulators is pipe hydraulics, particularly the pressure drop in the pipes of the reservoir's gathering and injection facilities. Accordingly, pressure drop must be calculated accurately in order to precisely monitor and simulate reservoir flow rates.
In existing reservoir simulators, pressure drop data for gathering and injection facilities such as well tubing connections are either obtained from a look-up, or VLP, table or by calculating the pressure drop using pressure drop correlations. In the first approach, VLP tables are calculated by a program external to the simulator using pressure drop correlations. The VLP tables are multidimensional, providing pressure drop as a function of several variables. These variables typically include the surface flow rate of one phase, ratios such as water cut and gas/oil ratio, the pressure at one end of the pipe, and, for compositional simulations, some measure of compositional variation, such as key component mole fraction or mean molecular weight. This approach does not fully capture the dependence on the composition of the fluid (i.e., the mole fraction of each component in the fluid, which limits the usefulness of VPN tables for compositional simulations.
In the second approach, pressure drops are calculated during the simulation, using pressure drop correlations, so the compositional dependency is fully captured. However, this can be computationally expensive because the calculations must be performed numerous times during the simulations as the flow rates, fluid composition, and pressure change even if the values for flow rates, composition, and pressure are similar to previous calculations.